Some time spent at home ordering materials, vacuum pump equipment etc. Returned to the boat yesterday, and today continued preparation including making cardboard templates for the smaller cut outs on the port and starboard side.
Next step will be to make plywood templates, and hopefully use these to make marine ply backing plates instead of the balsa core.
The plan is still to use epoxy resin to glue the final balsa and marine ply core, however, it is likely that a polyester resin will be used to replace the inner laminate. The first reason for this is, apparently if you undertake a repair with different material to the original it can invalidate you insurance unless approved by a marine surveyor. Secondly epoxy resin layup can be brittle, where as polyester layup has more flex. The transom does flex with the wind generator running.